Reappearing gun sight
Advance to time index 0:30:31 and you will see that there is no gun sight on the tip of Billy's gun. However, at time index 0:30:32 there is a gun sight at the tip of the gun. The gun sight disappears again at time index 0:30:35, reappears at 0:30:37, then disappears again at 0:30:39.